Digoxin Toxicity

What to do right now

1. Call 911 for fainting, chest pain, confusion, severe weakness, or a very slow or irregular pulse.
2. For a mistaken extra dose without symptoms, call Poison Control at 1-800-222-1222 (US).
3. Do not take the next dose of digoxin until a doctor advises.
4. Bring all your medicine bottles to the hospital.

How digoxin works and why it becomes toxic

Digoxin strengthens heart contractions and slows the heart rate by acting on the sodium-potassium pump in heart cells and increasing vagal nerve activity. These same actions, in excess, make heart cells irritable and slow electrical conduction.

Digoxin is cleared mainly by the kidneys and has a long half-life (about 36 to 48 hours with normal kidneys). Anything that reduces kidney function causes it to build up.

Risk factors

• Kidney problems: chronic kidney disease or sudden kidney injury from dehydration, vomiting, diarrhea or illness.
• Older age and low body weight.
• Electrolyte imbalances: low potassium (often from diuretics), low magnesium and high calcium all increase sensitivity to digoxin.
• Interacting medicines: amiodarone, verapamil, diltiazem, quinidine, some antibiotics (clarithromycin, erythromycin), some antifungals, and spironolactone can raise digoxin levels.
• Hypothyroidism and severe lung disease.
• Dosing errors: taking an extra dose or confusing tablet strengths.

Symptoms

Gastrointestinal

• loss of appetite, often the earliest sign
• nausea and vomiting
• abdominal pain and diarrhea

Nervous system and eyes

• tiredness and weakness
• confusion, delirium or hallucinations, especially in older adults
• blurred vision, seeing halos, or colors tinted yellow or green (xanthopsia)

Heart

• palpitations or a slow heartbeat
• dizziness and fainting
• almost any arrhythmia, from extra beats to heart block, atrial tachycardia with block and ventricular tachycardia

Acute vs chronic toxicity

Diagnosis

• ECG: to detect rhythm problems. Characteristic "scooped" ST segments show digoxin effect but do not by themselves mean toxicity.
• Blood digoxin level: best measured at least 6 hours after the last dose. Toxicity is a clinical diagnosis: symptoms can occur at "normal" levels, especially with low potassium.
• Potassium, magnesium and calcium.
• Kidney function.

Treatment

• Stop digoxin and any interacting medicines.
• Continuous heart monitoring.
• Correct electrolytes: replace potassium and magnesium if low; treat high potassium in acute poisoning.
• Digoxin-specific antibody fragments (DigiFab): an antidote that binds digoxin and reverses toxicity within 30 to 60 minutes. Used for life-threatening arrhythmias, very high potassium, very high levels, or large ingestions.
• Activated charcoal: may be given soon after an acute overdose.
• Atropine or temporary pacing for very slow heart rates.

Prevention

• Take digoxin exactly as prescribed, at the same time each day. Use a pill organizer.
• Keep regular appointments for blood tests of kidney function, potassium and digoxin level.
• Tell every doctor and pharmacist that you take digoxin before starting new medicines, including antibiotics and supplements.
• Contact your doctor if you have vomiting, diarrhea or are not eating or drinking well, as dehydration can cause levels to rise.
• Store medicines away from children.

Outlook

Most people with digoxin toxicity recover fully with prompt treatment. Severe toxicity with arrhythmias can be fatal without treatment, but the antidote is highly effective. After recovery, doctors review whether digoxin is still needed and at what dose.

Frequently asked questions

What are the early signs of digoxin toxicity?

Early signs include loss of appetite, nausea, vomiting, tiredness and confusion. Some people notice blurred vision, halos around lights or a yellow-green tint to their vision. Palpitations, dizziness or a slow pulse suggest effects on the heart and need urgent care.

What causes digoxin toxicity?

The most common causes are worsening kidney function, often from dehydration or illness, low potassium from diuretics, interactions with medicines such as amiodarone or verapamil, older age, and dosing mistakes.

Is there an antidote for digoxin toxicity?

Yes. Digoxin-specific antibody fragments, often called DigiFab, bind to digoxin and reverse its effects within an hour. They are given in hospital for serious toxicity, such as dangerous heart rhythms or very high potassium.

What is a toxic digoxin level?

Levels above about 2 ng/mL are generally considered toxic, but toxicity can occur at lower levels, especially with low potassium or magnesium. For heart failure, doctors usually aim for lower levels, around 0.5 to 0.9 ng/mL. Symptoms matter more than the number alone.